That crowd has a very nasty habit of demonizing democrats, while at the same time backing an independent running for the endorsement of the democratic party.
Theres a sense of entitlement that only the sanders crowd knows what's best for the party and the country, while at the same time doing jack fucking shit to canvass, raise funds, or otherwise assist any candidates running below the presidential level.
Local politics- your state reps, senators, city councilmen etc are absolutely crucial in how the lives of everyday people are affected but the sanders wing is nowhere to be found when it's time to put the work in to get people elected and supported.
I attended DSA meetings. Several in fact. The rhetoric is over the top nonsense about how democrats are the problem, democrats are in love with capitalism, and democrats need to be saved from themselves...presumably by sanders and his wing.
This rhetoric has not gone unnoticed, the lack of downballot support has not gone unnoticed (from Sanders AND his supporters), and consensus among the democratic base is that these people can die in a fire.